Fine structure collision strengths and line ratios for [Ne V] in infrared and optical sources

TL;DR

This paper provides improved collision strengths for Ne V transitions in infrared and optical wavelengths, with detailed calculations revealing significant differences at low temperatures and potential explanations for observed line ratio anomalies.

Contribution

It presents new Breit-Pauli R-Matrix calculations for Ne V, including near-threshold resonances, and analyzes their impact on line ratios in low-density plasma conditions.

Findings

Significant differences in collision strengths at T_e < 10000 K compared to previous data.

Variation in the 14/24 micron line ratio under low-energy-density conditions.

Potential explanation for anomalous mid-IR line ratios in planetary nebulae and Seyfert galaxies.

Abstract

Improved collisions strengths for the mid-infrared and optical transitions in Ne V are presented. Breit-Pauli R-Matrix calculations for electron impact excitation are carried out with fully resolved near-threshold resonances at very low energies. In particular, the fine structure lines at 14 micron and 24 micron due to transitions among the ground state levels 1s^22s^22p^3 (^3P_{0,1,2}), and the optical/near-UV lines at 2973, 3346 and 3426 Angstrom transitions among the ^3P_{0,1,2}, ^1D_2, ^1S_0 levels are described. Maxwellian averaged collision strengths are tabulated for all forbidden transistion within the ground configuration. Significant differences are found in the low temperature range Te < 10000 K for both the FIR and the opitcal transitions compared to previous results. An analysis of the 14/24 line ratio in low-energy-density (LED) plasma conditions reveals considerable variation; the effective rate coefficient may be dominated by the very low-energy behaviour rather than the maxwellian averaged collision strengths. Computed values suggest a possible solution to the anomalous mid-IR ratios found to be lower than theoretical limits observed from planetary nebulae and Seyfert galaxies. While such LED conditions may be present in infrared sources, they might be inconsistent with photoionization equilibrium models.